Two input combiner having useful and dummy load outputs

ABSTRACT

A four-port combining network which utilizes a single transformer element. The two input ports are supplied with radio frequency signals of the same frequency and phase. One output port is connected to a useful load such as an antenna. The other output port is connected to a dissipative &#39;&#39;&#39;&#39;dummy&#39;&#39;&#39;&#39; load. Under normal operating conditions the two input signals add to provide a single high power output and essentially no signal is fed to the dummy load. In the event of failure of one input signal the remaining operating input signal is divided between the two output ports. Respective isolation under all conditions is maintained between the two inputs ports.

United States Patent [191 Covill [451 July 17, 1973 TWO INPUT COMBINERHAVING USEFUL AND DUMMY LOAD OUTPUTS [75] inventor: Dennis H. Covill,Nova Scotia,

' Canada [73] As'signee: Nautical Electronics Laboratories Limited, NovaScotia, Canada [22] Filed: Nov. 2, 1971 I 211 Appl. 190.; 194,985

[ 52] U.S. Cl 333/6, 333/11, 336/181 [51] Int. Cl. H0311 7/48 [58] Fieldof Search 333/6, 8, 11; 336/171, 181

[56], r References Cited 3 UNITED STATES PATENTS 3,037,173 5/1962Ruthroff 333/11 FOREIGN PATENTS OR APPLICATIONS 329,905 1/1952 .Germany.333/11 Primary Etaminer-Paul L. Gensler Attorney-Christopher Robinson eta1;

[5 7] ABSTRACT A four-port combining network which utilizes a singletransformerelement. The two input ports are supplied with radiofrequency signals of the same frequencyand phase. One output port isconnected to a useful load such as an antenna. The other output port isconnected to a dissipative dummy" load. Under normal operatingconditions the two input signals add to provide a single high poweroutput and essentially no signal is fed to the dummy load. in the eventof failure of one input signal the remaining operating input signal isdivided betweenthe two output ports. Respective isolation under allconditions is maintained between the two in puts ports.

3 Claims, 2 Drawing Figures TWO INPUT COMBINER HAVING USEFUL AND DUMMYLOAD OUTPUTS FIELD OF THE INVENTION 7 This invention relates to animproved four-port combiner used to combine two synchronous, coherent ACsignals to form a single AC signal.

Known combining networks can be broken down into two categories. Thefirst category contains combiners usedto combine narrow band signals andcomprises one quarter wave transmission line sections arranged generallyin the form of a bridge circuit. The second category of combiningnetwork and the category in which the present invention is contained,includes the four-port transformer-wound, broad-band combiner. As inthefirst category, the transformers are generally arranged ina bridgecircuit. An example of the combiners of the second category is describedin US. Pat. No. 3,503,016, which issued to A.F. PODELL on 24 Mar. 1970.

Known broad-band combining networks have the disadvantage that they arerelatively complicated arrangements of a plurality of individualtransformers. The individual windings of these transformers must be.capable of handling the power output of one of the inputs. In contrast,the combiner of the present invention utilizes a single transformerhaving three windings and therefore represents a considerablesimplification of known prior art devices. The individual windings ofthe combiner in accordance with the present invention needv only becapable of handling a fraction of the power of either input and in factduring normal operating conditions, onlya fraction of the power outputof an individual source.

SUMMARY OF THE INVENTION In accordance with the present invention thereis provided a combiner network comprising an output port having a firstterminal and a second terminal for supplying a load, a first input porthaving first and second terminals, a second input port having first andsecond terminals, thesecond terminals of the said input ports and thesecondterminal of the output port being directly connected together; asingle transformer having a first winding and a second winding, thefirst winding being connected between the first terminal of the firstinput port and the first terminal of the output port, the secondwindingbeing connected between the first terminal of the output port andthe first terminal of the second input port, said windings beingoppositely wound .with respect to current flow from the first and secondinput ports and having a respective turns'ratio in inverse proportion tothe respective rated input powers of the first and second input portswhereby under rated operating conditions the net flux attributable tocurrent flow through said windings is substantially zero; dissipativeimpedance means having an impedance selected to balance rated loadimpedance and connected in a series loop with a third winding of saidtransformer, said third winding being mutually transformer-coupled withsaid first and second windings whereby, in response to non-zero net fluxin said windings caused by flux imbalance between said windings, saiddissipative impedance means is operative to dissipate a portion of thepower supplied by said input ports so as to maintain an impedancebalance between said input ports.

' signal will appear at both output ports 20 and 21. At

DESCRIPTION OF THE DRAWINGS The invention will be described in detailherein below with the aid of the accompanying drawings in which:

FIG. 1 is a schematic diagram of a known broadband, wound transformercombiner; and

FIG. 2.is a schematic diagram of a particular embodiment of a broad-bandcombiner according to the present invention.

DETAILED DESCRIPTION The combiner shown in FIG. 1 is comprised of twoindividual transformers l0 and 11. Transformer 10 has two primarywindings 12 and 13 and a secondary wind ing 14. Similarly, transformer11 has primary windings 15 and 16 and secondary winding 17. The combinernetwork is comprised of two input ports 18 and 19 and two output ports20 and 21. In operation, two coherent and synchronous AC signals areapplied to input ports 18 and 19.-The amplitudes of the signals need notbe the same but it is important that the frequency and phase'. of thetwo signals be identical. The current sense of the AC signals isindicated by the arrows leading away from input ports 18 and 19respectively. The currents circulating in the two primary windings 15and 16 of transformer 11 are wound in aiding sense and produce a netflux circulating in the magnetic core of transformer 11 whose intensityisproportional the sum of the two currents. As a result, there isinduced into the secondary winding 17 'of transformer 11 a current whichis proportional'to the sum-of the two individual input currents. Thissummation current is fed to a load R via output port 21. The same inputcurrents which additively combine in transformer 11 exactly oppose oneanother in transformer 10. The flux created by the current in winding 12is opposite in sense to the flux created by the current flowing inwinding 13. It can be seen that if the frequency and phase of the twoinput signals are identical, and the flux created by the two input portsare identical, there will be no net flux circulating in the magneticcircuit of transformer 10 and as a result, there will be no currentinduced into the secondary winding l4.-

However, if one of the input signals should fail, the power of theremaining input signal will be divided between the two transformers 10and 11 and the output such time, a dummy load" dissipative impedanceelement R will dissipate a portion of the remaining input signal. Inthis manner, the two input ports will remain mutually isolated.

A similar action takes place in the combiner according to the presentinvention, which is shown schematically in FIG. 2. However, it can bereadily seenthat the complexity of the circuit shown in FIG. 2 isconsiderably less than that shown in FIG. I.

Referring to FIG. 2, there are shown input ports 18 and 19 and outputports 20 and 21. Similar reference numerals are used for similarcomponents throughout the drawings. The combiner network comprises atransformer 30 having three mutually coupled windings 31, 32 and 33.Winding 31 is connected with source 19 and winding 32 is connected withsource 18 to obtain mutually opposing senses of current flow intransformer 30. Two coherent and synchronous AC signals are applied toinput ports 18 and 19 to produce signal currents whose instantaneoussense is represented by arrows.

The flux created in winding 31 by the current from input port 19 will beopposite in sense to the flux created in winding 32 by the currentflowing from input port 18. If the magnitude of the two fluxes isidentical, there will be no net flux circulating in transformer 30. Thiscriteria is satisfied if:

where N represents the number of turns of winding 31;

N represents the number of turns of winding 32;

and

i and i represents the two input signal currents. (Note that by properlyselecting the turns ratio, it-is possible to produce a zero net magneticflux in the transformer 30 by applying two input signals which are ofthe same frequency and phase but of different magnitudes.)

Since no net flux is normally (i.e., under rated operating conditions)present in the magnetic circuit of the transformer 30, the two inputcurrents add at the connection point 34 to produce an output currentsubstantially equal to the sum of the input currents at the output port21. This summation current is then fed to the load R When one of theinput signals fail, the remaining signal produces a net flux in thetransformer 30 and a cur rent is induced into winding 33, which in turnis absorbed by dummy load R via the output port 20. By properly choosingthe turns ratios in transformer 30, the combined effect of the newimpedance presented by the dummy load and the impedance created by theload R can be arranged to present, at the remaining operating inputport, an impedance equal to the impedance presented when both inputsignals were supplying current. In this manner, input ports 18 and 19are mutually isolated. I

The input impedanceof the circuit shown inFIG. 2 for input port 18 is:

ia Z1. azl N31) and the input impedance for port 19 is:

where Z, is the impedance of load R (The turns ratio for N and N isdetermined by the relative input power ratio to the two input ports byequation I, above.)

The isolation can now be obtained by the correct selection of the numberof turns N for the third winding, and the value Z,, of the dummy load RIf it is assumed that transformer 30 is an ideal transformer (i.e.having a unity coupling coefficient and negligible magnetizing current),the voltage transfer coefficient C from input port 18 to input port 19with input port 19 opencircuited is given as follows:

|s+1o ss 1. a: a: u) a:; ZL 32 n) It can be seen from equation 4 that nocoupling will be present, (i.e., C +19 will be zero), if Z 2,, (N 31We?) The condition for zero coupling from input port 19 to input port18, (i.e., C M8 0), is identical with the above result.

The transformer 11 shown in FIG. 1 must be capable of handling theentire power from the input ports 18 and 19. However, transformer 10,will, under the worst conditions only be required to handle one half ofthe power of the remaining input which has not failed. Under theseconditions, the power of the remaining input will be divided betweenboth transformers l1 and 10. In the combining network according to thepresent invention, as shown in FIG. 2, there is no one winding whichmust be capable of handling the complete power input of the two ports 18and 19. As a result, not only has one transformer been eliminated usingthe combining network according to the present invention but theremaining transformer may be reduced in size.

The embodiment of the present invention described above is concernedwith the objective of coupling together a number of coherent RF signalinputs to an antenna (the load). Clearly the frequency range for whichthe invention is useful will be limited by the operating characteristicsof available wire-wound transformers.

What I claim as my invention is:

l. A combiner network comprising an output port having a first terminaland a second terminal for supplying a load, a first input port havingfirst and second terminals, a second input port having first andsecondterminals, the second terminals of the said input ports and the secondterminal of the output port being directly connected together; a singletransformer having a first winding and a second winding, the firstwirlding being connected between the first terminal of the first inputport and the first terminal of the output port, the second winding beingconnected between the first terminal of the output port and the firstterminal of the second input port, said windings being oppositely woundwith respect to current flow from the first and second input ports andhaving a respective turns ratio in inverse proportion to the respectiverated input powers of the first and second input ports whereby underrated operating conditions the net fluxattributable to current flowthrough said windings is substantially zero; dissipative impedance meanshaving an impedance selected to balance rated'load impedance andconnected in a series loop with a third winding of said transformer,said third winding being mutually transformer-coupled with said firstand second windings whereby, in response to non-zero net flux in saidwindings caused by flux imbalance between said windings, saiddissipative impedance means is operative to dissipate a portion of thepower supplied by said input ports so as to maintain an impedancebalance between said input ports.

2. A combiner network according to claim 1 wherein the rated inputpowers of the first and second input ports are substantially the sameand the said first and second windings have substantially the samenumber of turns.

3. A combiner network as defined in claim 1, wherein tion at R.F. signalfrequencies.

t l i

1. A combiner network comprising an output port having a first terminaland a second terminal for supplying a load, a first input port havingfirst and second terminals, a second input port having first and secondterminals, the second terminals of the said input ports and the secondterminal of the output port being directly connected together; a singletransformer having a first winding and a second winding, the firstwinding being connected between the first terminal of the first inputport and the first terminal of the output port, the second winding beingconnected between the first terminal of the output port and the firstterminal of the second input port, said windings being oppositely woundwith respect to current flow from the first and second input ports andhaving a respective turns ratio in inverse proportion to the respectiverated input powers of the first and second input ports whereby underrated operating conditions the net flux attributable to current flowthrough said windings is substantially zero; dissipative impedance meanshaving an impedance selected to balance rated load impedance andconnected in a series loop with a third winding of said transformer,said third winding being mutually transformer-coupled with said firstand second windings whereby, in response to non-zero net flux in saidwindings caused by flux imbalance between said windings, saiddissipative impedance means is operative to dissipate a portion of thepower supplied by said input ports so as to maintain an impedancebalance between said input ports.
 2. A combiner network according toclaim 1 wherein the rated input powers of the first and second inputports are substantially the same and the said first and second windingshave substantially the same number of turns.
 3. A combiner network asdefined in claim 1, wherein said transformer and windings are selectedfor operation at R.F. signal frequencies.